In the covering of a flat roof surface, such a covering most commonly consists of a multiplicity of asphalt-impregnated felt or felt-like materials which are manufactured and sold in rolls of various widths and deposited on the roof in layers over an insulation layer.
Customarily, rolls of material are laid out in overlapping configuration. The layers of material, which may include waterproof and moisture resistent layers, are usually covered with a final layer of hot tar.
Blisters are an inevitable "product" of the application of roof surfaces. Gases or vapors, or both, are either entrapped between the various layers or are produced by a reaction of the various products, perhaps further induced by the heat of the sun on the roof.
It is known that internal pressures build up during the heat of the day and subside during the cool of the night. This creates an inevitable expansion and contraction, eventually resulting in the blistering. Such action is exacerbated by the heat of a midsummer sun or the chilling cold of winter.
Once a blister is formed, it will only grow with time until it eventually fractures. Once fractured, water will enter and, not only destroy the layered materials, but also result in leakage into the building.
For many years, and predominantly even now, the primary solution to the problem was an on-site inspection of the roof. If one or more blisters were discovered in a roof, those who maintained the roof had two choices. They would either monitor the blister and repair it when it eventually ruptured, or they could slit and fill and cover the blister with another layer and with tar.
Two problems are encountered. If maintenance is postponed, severe damage usually results when the blister fractures. If the blister is slit and repaired, there is no assurance that the blister will not reappear at or near the same spot.
Fairly recently, engineers employed by the Department of the Army have developed and patented a unique pressure relief valve which is used to solve the blister problem. This valve is the subject of U.S. Pat. No. 4,757,654. The problem and the solution are explained in detail in that patent, of which this Applicant is the exclusive licensee.
Briefly, the solution is a very tiny one-way valve, enclosed in a relatively flat housing having an elongated, relatively sharp, hollow shaft protruding downwardly therefrom and vented via a channel through the valve to the outside of the valve housing. This permits venting of gases or moisture and prevents the inward flow of water.
When a blister is found, the user inserts the valve housing directly into the blister. Alternative designs are disclosed.
Experimental use with the aforesaid device has disclosed that there are certain deficiencies in the structure. In actual operation, the smooth shafted devices have a tendency to pop out, and there is a tendency to separate the layers of roofing material when the threaded devices are inserted.
Further the multi-sectional housing, with its O-ring and chambers is extremely complicated in assembly and operation.
It is accordingly an object of this invention to create a blister vent which is much simpler in structure and of an improved design which overcomes the deficiencies mentioned above.